Science fiction has long contemplated the risk that our increasingly capable computers and robots could one day decide they'd be better off without us, or using us as their energy source. Now, philosophers and scientists at Britain's Cambridge University have proposed giving the question serious thought with a new Center for the Study of Existential Risk."It tends to be regarded as a flaky concern, but given that we don't know how serious the risks are, that we don't know the time scale, dismissing the concerns is dangerous," Cambridge philosophy professor Huw Price told the Associated Press.Here's a gallery of notable sci-fi examples of machines turning on humanity, starting with the "Terminator" movies, in which the Skynet computer system
becomes self aware and, after operators try to shut it down, decides to
take out humanity. Warning: This gallery is full of spoilers.

Photo: ANDY ROGERS, SEATTLE POST-INTELLIGENCER

Science fiction has long contemplated the risk that our...

Science fiction has long contemplated the risk that our... Photo-3802408.52995 - SFGate

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In 1984's "The Terminator," Skynet, nearly defeated, sends Terminator Arnold
Schwarzenegger back in time to kill the mother of resistance leader John
Connor before Connor is born.

Here are the bad robots taking over in a scene from "Terminator 3: Rise of the Machines."

Photo: Warner Bros. Pictures

Here are the bad robots taking over in a scene from "Terminator 3:...

Here are the bad robots taking over in a scene from... Photo-3797679.52995 - SFGate

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In the "Matrix" films, the intelligent machines have taken over, turning humans into an energy source and keeping them docile in a computer simulation of the world as it was in 1999, the year the first movie in the franchise came out. The main computer enforcer within this virtual world is Agent Smith (Hugo Weaving), right, shown fighting human hero Neo, played by Keanu Reeves.

In 1983's "War Games," Matthew Broderick's character hacks into a computer that he doesn't realize is at NORAD and starts a "game" of "Global Thermonuclear War." The computer -- WOPR (War Operation Plan Response), AKA Joshua -- isn't trying to kill anyone, per se. It just almost starts a global nuclear holocaust while trying to win the game.

The Cylons, from "Battlestar Galactica," are a classic example of intelligent robots trying to kill us. The Cylons in the original TV show, from 1978 and 1980, had been created by a race of the same name, which then died out.

Photo: MARK RALSTON, AFP/Getty Images

The Cylons, from "Battlestar Galactica," are a classic example of...

The Cylons, from "Battlestar Galactica," are a classic... Photo-3802326.52995 - SFGate

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In the "Battlestar Galactica" remake, which debuted in 2003, humans created the Cylons as workers.